1. Field of the Invention
The present invention relates to a magnetoresistive effect element in a current perpendicular to plane type (CPP-type) structure that detects a magnetic field intensity as a signal from a magnetic recording medium, and so on, a thin film magnetic head with the magnetoresistive effect element, and a head gimbal assembly and a magnetic disk device that have the thin film magnetic head.
2. Description of the Related Art
In recent years, with an increase in the longitudinal recording density of a magnetic disk device, there have been growing demands for improvements in the performance of a thin film magnetic head. For a thin film magnetic head, a composite type thin film magnetic head has been widely used; it has a structure where a reading head having a read-only magnetoresistive effect element (hereinafter often called the MR element for short), and a recording head having a write-only induction type electromagnetic conversion element are laminated together.
An MR element, for instance, includes an AMR element making use of an anisotropic magneto-resistive effect (AMR), a GMR element making use of the giant magneto-resistive effect (GMR), and a tunnel type magneto-resistive effect (TMR) element making use of the tunnel type magneto-resistive effect (TMR).
A reading head especially requires high sensitivity and high output characteristics. A GMR head with a GMR element in a spin valve type has already been mass-produced as a reading head capable of meeting these demands. Recently, a reading head with the TMR element has also been mass-produced for further improving the longitudinal recording density.
In view of the improvement of a SN ratio (signal-to-noise ratio), a next generation GMR element in a CPP-type structure (CPP-GMR element) is already being developed in which a sense current is applied in a perpendicular direction (laminated direction) to each layer surface formed for the GMR element.
A spin valve type CPP-GMR element includes a laminated structure having a conductive nonmagnetic intermediate layer, and a first ferromagnetic layer and a second ferromagnetic layer, which are separated by the conductive nonmagnetic intermediate layer. A typical spin valve type CPP-GMR element is formed by a laminated structure for its main layers as follows: a lower electrode/an antiferromagnetic layer/a first ferromagnetic layer/a nonmagnetic intermediate layer/a second ferromagnetic layer/an upper electrode. A magnetization direction of the first ferromagnetic layer, which is one of the ferromagnetic layers, is pinned in the perpendicular direction to a magnetization direction of the second ferromagnetic layer when the externally applied magnetic field is zero (0). The magnetization direction of the first ferromagnetic layer can be pinned by making an antiferromagnetic layer adjacent thereto and providing unidirection anisotropic energy (also referred to as “exchange bias” or “coupling magnetic field”) to the first ferromagnetic layer by means of exchange-coupling between the antiferromagnetic layer and the first ferromagnetic layer. For this reason, the first ferromagnetic layer is also called a pinned layer. In this element, a smaller cross sectional area of an element has a larger resistance value. Namely, it is an appropriate structure for, so called, a narrower track that narrows a track width.
In order to have the recording density, 1 Tbits/in2, as a next generation element, it is required that the size of an element is 25 nm×25 nm or smaller. In order to decrease the resistance of an element, it is required that the AR (Area Resistivity) of an MR element is 0.3Ω·μm2 or lower.
To comply with these demands, in a CPP-type element, which has a nonmagnetic intermediate layer of a three-layer structure, Cu/ZnO/Cu, and is processed at a temperature of 250° C. or lower, it is disclosed that an appropriate area resistivity (AR) and high MR value are realized (Japanese laid-open patent publication number JP2008-91842). ZnO is generally known as an N-type semiconductor characteristic because of the existence of zinc as an interstitial atom and an electron emitted from an oxygen deficiency.
However, if the element characteristics for over 1 Tbits/in2 recording density are considered, the requirement to improve an MR ratio is unlimited. Therefore, a proposal of new and original technology that achieves a further improved MR ratio is required.
With the consideration of the situation described above, the present invention is provided. The object of the present invention is to provide an MR element in a CPP-type structure that further improves an MR ratio.